Compositional effects and optical properties of CdSeXTe1-X alloyed nanotube arrays

Well-aligned CdSeXTe1-X nanotube arrays with X ranging from 0 to 1 have been prepared on ITO substrates. The alloyed nanotubes are composed of many nanocrystals with a ZB structure, and the outer diameter and wall thickness are within 270-510 nm and 30-80 nm, respectively. As the cell constant decreases with the addition of Se due to its smaller atomic diameter than Te, the band gap of the alloys also presents a nonlinear behavior, which enables CdSe0.30Te0.70 and CdSe0.44Te0.56 to have respective band gaps of 1.46 eV and 1.44 eV, much narrower than those of pure CdSe and CdTe. Raman scattering has been demonstrated for the alloyed nanotubes, wherein LO and SO phonon vibrations similar to those in CdSe and CdTe have been detected. Especially, the intensity of the SO mode is much stronger than that of the LO mode for CdSe0.30Te0.70 and CdSe0.44Te0.56 nanotube arrays due to the alloying compositional disorder related to grain boundaries or defects. Based on the lattice constant changes and Raman vibration shifts, the contributions to the band gap bowing have been demonstrated.